<!DOCTYPE html>
<html lang="en">
  <head>
    <title></title>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">

  </head>
  <body>
  <input type="text">
  </body>

<script>
  var bb=[];
  bb[3]=3,

   JSON.stringify(bb)
   console.log(bb)
   alert(bb)
</script>

  
</script>
</html>